How can I get the name of the class object as a string?

I am writing a method in a class which returns the name of a class object which was previously created using certain settings. So I need to know how do I extract only the name of the object created for those settings. Any help is appreciated!

[Adam]

Why on earth would you want to do this?! Objects are just variables whose name is relevant within their scope for readability purposes but carries no meaning whatsoever from the pure code perspective. A class should never be containing methods that try to work out what name was given to the objects of it that were created. If an object needs a name then add a 'name' property to the class itself and use that.

[Apoorva Nagendra]

I asked it because I need it. I cannot tell you why I need it, but I do.

[J. Alex Lee]

Agreed that it seems a messy way to achieve whatever purpose ultimately in mind. But let's not say "never should be done" to anything. Maybe some better way will come out of it.

I'm not sure the "name property" itself will be useful in your objective, but maybe you can define a static/persistent variable shared by members of the class that tracks instances of the class by populating it in the constructor. Your lookup method can then query that table, rather than querying the outside world.

[Steven Lord]

How do you want to handle the scenario where the class object was previously created in a different MATLAB session, saved in that session, and loaded in the current session? If the object was originally created in that first session "using certain settings", do you also consider the instance of that object loaded in the current session to have been created the same way?

It sounds like you want each object to record how it was constructed in a property of the object itself, and for your code to be able to query that property. That's possible (using an immutable property) but it also seems like it could be extremely complicated and potentially fragile depending how complicated your class is.

[Stephen23]

"I asked it because I need it. I cannot tell you why I need it, but I do."

So far every other time that someone has posted here saying "I need to magically access variable names" it has turned out to be incorrect and inefficient (in the sense that other ways of doing their task are simpler, faster, and less buggy):

https://www.mathworks.com/matlabcentral/answers/105936-how-to-make-dynamic-variable-names-a1-a2-an-with-for-loop-using-eval-num2str#answer_332454

So far you have not provided us with any reason to believe that this will be any different: I am genuinely interested to know this use-case is, that you require this kind of meta-programming. Please give some details!

[Adam]

From an object-orientation perspective, until I see a clear case otherwise I would stand by that 'A class should never be containing methods that try to work out what name was given to the objects of it that were created'.

Obviously if I see or hear of a counter-example I would reconsider, but it seems so fundamentally against program design that 'never' seems fair enough given it is only my opinion I am stating anyway. I can easily believe that design mistakes (of which I have made uncountably many) can lead to situations where this may seem like something that is needed, but at that point it is time to take a step back and re-examine the design decisions that got you to that point in the first place rather than just plough on through to whatever end.

Answer 1

[J. Alex Lee]

One way I can think of is to use "evalin('base',...)" for your method to probe all the base workspace variables to check their properties (which is what I assume you mean by "settings"):

 varlist = evalin('base','whos')
 for i = 1:length(varlist)
   if isa(varlist(i).class,myClassName)
      % code to check property values or settings
   end
 end

[J. Alex Lee]

Just also occurred to me that the result of whos could be passed as an argument to the method to eliminate need for "evalin".

[Apoorva Nagendra]

I will try both the options and get back on which worked best. Thank you so much for your help!

Answer 2

[Jan]

This sounds like meta-programming. If the actual program requires information about the implementation of the code, the complexity of the code is prone to exploding. Therefore meta-programming is often considered as a programming-anti-pattern, because if produces more problems than it solves.

Peeking with evalin in the caller's or base workspace fails, if the part of the code is moved to a subfunction. It is much cleaner not to include dependencies to the location of the code.

What about implementing a list a objects together with the required values? a very simple form of this method is using structs, where the fieldnames are stored easily also without any meta-programming. I still assume, that the need for accessing the names of objects is a confusion of the levels of data and code. It might be a massive simplification, to store names and data in lists instead of creating a connection to the details of the code.